Field of the Invention
Aspects and embodiments of the invention are most generally directed to an optical imaging system, methods pertaining thereto, and applications thereof; more particularly to a panoramic optical imaging system, methods pertaining thereto, and applications thereof; and, most particularly to a panoramic optical imaging system that has zero or substantially no parallax, methods pertaining thereto, and applications thereof.
Description of Related Art
Current 360 degree systems without parallax employ an arrangement of mirrors to scan the image and are limited by an imaging speed of 10 frames per second (fps). Google uses a 360 degree camera with refractive lenses developed by Immersive Media to capture photos for its Streetview software. The photos must be post-processed and corrected for parallax, costing time, which reduces Google's ability to scale its Streetview initiatives. Fisheye lenses provide wide angle imaging but at the cost of high distortion. Distortion is the physical result of mapping a large spherical object onto a small flat image plane.
Some companies have developed optical systems to simplify the process of taking a panoramic image. Rather than rotating the camera to get multiple shots, all of the photos are captured simultaneously with many cameras imaging different parts of the scene. Immersive Media and Greypoint Imaging have developed single shot 360 degree cameras that are available for varying price tags between $10,000 and $100,000. Both companies develop software to automatically correct for the artifacts (parallax) created in the image and offer a better solution than panoramas captured by one camera, e.g., the iPhone camera. The software, however, is not perfect and many artifacts still exist in the images. Anecdotally, Google, had one person carry a Dodeca 360 camera (offered by Immersive Media) around the Grand Canyon, and had to employ programmers to correct the images frame by frame for the artifacts induced by parallax.
Parallax and the Chief Rays of an Optical System
Parallax is defined as “the effect whereby the position or direction of an object appears to differ when viewed from different positions, e.g., through the viewfinder and the lens of a camera.” Parallax is created as a result of stitching together images from multiple cameras, each with its own unique perspective of the world.
Referring to FIG. 1, the chief ray of an optical system is the meridional ray that starts at the edge of an object, crosses the center of the optical axis at the aperture stop, and ends at the edge of the image at the detector. Thus the chief ray defines the size of an image.
The chief ray plays a critical role in the parallax created by stitching together multiple images. FIG. 2 illustrates two optical systems (cameras) side by side. For the lens unit on top, the square, triangle and rectangle are mapped to the same point in the image, whereas for the lens unit on bottom they are mapped to three distinct points as shown. In the top imaging system, they are imaged by the same chief ray, whereas for the bottom imaging system, they are imaged by three distinct chief rays. When combining the two images in FIG. 3, parallax would occur and an image as shown in FIG. 4 would result.
The search for an algorithm that can correct for parallax has been going on for many years. Many solutions have been developed but even with the most sophisticated algorithms to date, artifacts are still left in panoramic images. For some, this may not be a problem as software engineers can be hired to fix the images frame by frame; however, for the general consumer this option of correcting each image is not feasible. A better solution is needed that effectively corrects for parallax before such a system can be made available to the consumer market. It is preferable to solve the problem of reducing parallax in an image optically, rather than computationally.
Current designs created for single shot panoramic imaging suffer from parallax because they are created from imaging systems with overlapping fields of view. FIG. 5 is taken from U.S. Pat. No. 2,696,758. This figure illustrates how parallax is created in the 360 degree imaging systems available today. The field of views overlap and a triangle that appears at the edge of the FOV for the bottom lens system will appear at around 0.707 times the FOV in the imaging system on top. Thus, the triangle is mapped to different image points for each camera. On the bottom it is mapped to the full FOV (the edge of the image).
The inventor has thus recognized the advantages and benefits of a panoramic imaging system and associated methods in which there is no parallax, and where the parallax is eliminated optically rather than by post-processing software. Such a system would have applications including providing a scalable way to map the streets of the planet; allowing for the creation of virtual tours, both of cities and of private institutions; high frame-rate video surveillance; military applications including drone and tank technology; an alternative for fisheye lenses which provide wide angle imaging at the cost of high distortion.